Ligands featuring a 1,1 '-bis(donor)ferrocene motif can adopt various binding modes.
Among them, the kappa 3 binding mode, which involves interaction between the iron
center of the ferrocene unit and the transition metal is the most unique. Although
various examples highlight the interaction itself, the exact quantification of its
strength remains uncertain. In our computational study, we systematically investigate
the nature of this unique heterometallic bond, demonstrating that the electron density
at the transition metal primarily governs the heterobimetallic interaction. On the
other hand, the contribution of the ipso-carbon atoms of the cyclopentadiene ring
is not negligible. We demonstrated that isodesmic reactions provide the most quantifiable
data regarding the interaction. If the transition metal center is complexed with good
electron-donor ligands or its positive charge is compensated by the negative charge
of the ligands, the interaction with the electron-rich iron center recedes into the
background. Finally, we highlighted the importance of the accurate computational description
of these systems.
